Method for cleaning (degreasing) web material

ABSTRACT

IN DEGREASING STEEL ARTICLES AN IMPROVEMENT IN OVERALL COST AND IN CONVENIENCE IS REALIZED BY DISPLACING OILY SUB: STANCES FROM THE STEEL BY THE USE OF DETERGENTS HAVING A HYDROPHOBIC BALANCE OF 10 AND ABOVE, RESULTING IN THE FORMATION OF A LABILE EMULSION.

May 14, 1974 B. LINDGREN 3,310,786

METHOD FOR CLEANING (DEGREASING) WEB MATERIAL Filed April 16, 1971United States Patent Ofice 3,810,786 Patented May 14, 1974 3,810,786METHOD FOR CLEANING (DEGREASING) WEB MATERIAL Boris Lindgren,Eskilstuna, Sweden, assignor to Nyby Bruks Aktiebolag, Nybybruk, SwedenFiled Apr. 16, 1971, Ser. No. 134,742 Int. Cl. B08b 7/04 US. Cl. 134-9 8Claims ABSTRACT OF THE DISCLOSURE In degreasing steel articles animprovement in overall cost and in convenience is realized by displacingoily substances from the steel by the use of detergents having ahydrophobic balance of and above, resulting in the formation of a labileemulsion.

At the rolling of web material, particularly of stainless steel,necessarily oil is used. After completed rolling, this oil must beremoved very carefully from the web surfaces as otherwise, particularlyat subsequent annealings, surface reactions would occur which result ina partial or total rejection of the material.

The conventional method, which at present is the only possible one,comprises in principle the steps of removing the oil in a chemical andmechanical way by washing the surfaces in a liquid, usually water, whichadvantageously is heated and to which grease or oil solving chemicalsare added. For intensifying the solvating effect of chemical agents, thechemical attack is combined with a mechanical effect which, for example,most easily can be achieved by brushing. Thereby the solvent is broughtinto a more intimate contact with the impurities. This operation usuallyis followed by flush cleaning and drying. The conventional method hasseveral disadvantages, of which by way of example the following ones maybe mentioned:

1) The addition of detergents or solvents provides the emulsion of waterand oil with a high stability, i.e. the oil cannot be separated. Thismeans frequent changes of the washing solution.

(2) For reducing the number of washing solution changes, very largequantities of washing solution are to be applied in order thereby to beable to clean large amounts of web material until that concentration ofoil and impurities is obtained at which the effectiveness of thedetergent decreases. Said large quantities require voluminous, bulkymeans-i.e. vessels-with high space requirements, particularly in theirlongitudinal extension, and also large and power demanding auxiliaryequipment, for example for brushing, pumping etc. A further consequenceis the problem connected with taking care of heavily polluted washingsolutions at their discharge.

(3) The detergents used in relatively large quantities include largeamounts of alkali, phosphates, silicates, hydrates and carbonates. Thesedetergents are chemically labile, i.e., they disintegrate and therebylose their solvating effect and constitute a heavy load for theefliciency degree of installation. This applies particularly to thepolyphosphates, which have a very high thermolability. This implies thatthese polyphosphates disintegrate to orthophosphates and lose theirsolvating effect. Their emulsifying effect, however, results inemulsions of oil and water of high stability.

(4) The high stability of the resulting emulsion impedes the separationof the oil from the emulsion. This in its turn renders it impossible toutilize a circulation system with a theoretically unlimited use of thewashing solution, i.e. if it were possible to reduce or eliminate thevery rapidly increasing degree of pollution and the concentration ofoil.

(5) For achieving an effective cleaning, usually about 3% of a veryexpensive detergent, counted on the relatively large water quantity,must be added. The high concentration implies that large amounts ofemulsion and detergent remain on the surfaces of the cleaned webs andare to be removed by washing and flushing, in many cases by means ofbrushes. The result is satisfactory only in a few cases, because thedegree of cleanliness obtained is not perfect. This involves thedisadvantage that remainders of detergent and oil may react with the websurface. It is therefore necessary to apply much flushing water, whichin its turn requires pumping systems and installations for mechanicalcleaning (brushing installations) as well as means for the supply andremoval of said large flushing water quantities. It is particularly thealkali content in the solvent which is dangerous for the surface of thecleaned web. Alkali remaining after the flushing constitutes a risk ofcorrosion.

(6) The large and space-requiring installation is difficult to operatein its entirety, it requires a relatively large operation staff anddemands much service, etc. With respect to service, it is particularlythe control of the chemical composition which has to be madecontinuously because of the different consumption of the differentcomponents in the solution. It is, thus, not the proportion of detergentin its entirety which is to be controlled, but the proportion of thedifferent components in the detergent, in order to ensure a troublefreeoperation.

A further relatively effective method among those applied for theremoval of the oil is the trichloroethylene degreasing method. Thismethod, however, has the dis advantages as follows.

( 1) The installation costs are relatively high.

( 2) The health problems are difficult.

(3) The trichloroethylene remaining on the sheet metal surfaces givesrise to inconveniences at the heat treatment (carbon pickup). Thisapplies particularly to stainless sheet metal.

(4) Trichloroethylene is an expensive product, and its consumption ishigh.

(5) The method of using trichloroethylene is not adapted for use at websin motion, because it does not meet the requirement of perfect sealing.

The method and the apparatus according to the invention have as theirobject to eliminate the aforesaid disadvantages of the knownconventional methods. The invention in principle is characterized by adisplacement of the oil in a chemical-physical way, which displacementis effected by the use of detergents with ahydrophylic-lypophylic-balance (HLB) of 10 and above, which results inthe formation of a labile emulsion, which by constructional meansaccording to the invention very rapidly disintegrates to oil and water.

The method operates in principle with the characterizing features asfollows.

The specially selected detergent can form with water and oil an emulsiononly when energy is supplied and the energy level is maintained. As soonas the energy supply ceases, the emulsion reassumes its labile nature,the oil coalescence proceeds rapidly and totally, so that the oil isseparated from the water and can be returned to a normal use, forexample as fuel oil. Subsequent to the coalescence the detergent isregenerated automatically, and the washing solution free of oil canagain be supplied into the process.

The apparatus for carrying out the method according to the invention ischaracterized by means for the supply of energy and an arrangement-theso-called rest roomwhere the quasi-stable emulsion due to the absence ofenergy reassumes its labile nature, so that the separation of the oilfrom the washing solution can take place.

In the following the construction of an installation and the function ofthe method is described by way of example, with reference to theaccompanying figure.

From the working station (not shown) which may be, for example, arolling mill, a grinding machine, polishing machine or the like, whereoils or the like are applied to or develop on the surfaces, the webpasses through a pair of doctor rolls 1, which under pressure removerolling oil, for example, to such a degree, that the web only shows acoherent oil film without puddles and runnels. The doctor rolls aremade, for example, of metal and coated with felt or plastic, butadvantageously with rubber. Below the rolls is provided a collectingvessel (not shown) with flutes for the oil.

The web thereafter enters the degreasing zone 2 and passes in turn by aspray ramp 3 spraying a detergent solution onto both surfaces of theweb, an energy supply means, which in the example shown is in the formof circular rotary brushes 4 vigorously agitating the washing solutionon both surfaces of the web, and a spray ramp 5 for flushing both websurfaces with a clean detergent solution. The detergent solutionincludes water plus an addition of 0.05% by weight of a detergent withan HLB value at or above 10, for example nonyl-phenolethylene oxideadduct (which is a wetting agent with a relatively high HLB value andwith a hydrophilic nature). As detergent there is used one (such as thementioned nonyl-phenol-ethylene oxide adduct) having a non-ioniccharacter, taken alone or in combination with an anionic and/or acationic detergent. The amount of the selected detergent used in theaqueous solution is from 0.001% to 1.0% by weight; advantageouslyhowever, from 0.001% to 0.1% by weight and particularly to 0.05% byweight. The HLB value states the hydrophilic-lypophilic-balance in thechemical composition of a detergent and, thus, is a classification valuefor detergents with respect to the solubility in oil or water. The valueis a limit value at which the detergents change their nature, i.e.change over from oil solubility to water solubility. This detergentsolution advantageously may have a temperature of about 60 C., at whichthe solution speed is greatest, particularly when waxes or similarsubstances have been applied to the sheet metal surface at working (forexample at polishing).

The web passes after the degreasing zone again through a pair of doctorrolls 6, which under a relatively high pressure remove the film ofdetergent solution. Thereafter the web is ready for further working orreeling. With respect to the film of detergent solution remaining afterthe passage of the web through the doctor rolls, it may be mentionedthat this film has no damaging effect at the further working,particularly at annealing.

The detergent solution is supplied from a sedimentation-storage tank 7by pump 8 to the aforementioned spray system in the brushing andflushing zones. In both of said zones, a relatively high energy amountis supplied to the solution and thereby imparts to the solution atemporary emulsion stability (quasistability), which contributes tolifting the oil remaining on the web therefrom and emulsifying it. Theemulsion is pumped, by pump 8, from a collecting vessel 9 in directconnection with the degreasing zone to the aforesaidsedimentationstorage tank, the so-called rest room. Heat is supplied tothe rest room and through the degreasing operation, at between 30 C. and80 0, preferably between 50 C. and 70 C., and suitably at about 60 C.through means (not shown) and facilitates, as mentioned above, thedegreasing and also promotes the separation of the oil from the water.Within the tank proper are provided service means, such as an oilseparator 10, level controls (not shown) with metering pump fordetergents, thermostats and filters. In the drawing the oil separator isshown by its simplest embodiment, viz. as a partition wall. At

very high requirements on cleanliness, or for emulsions with very finedroplets as well as at highly limited liquid volumes, advantageously acoalescence filter is applied, either in combination with said rest roomor without the same.

In connection with the example described, the following may bementioned.

The detergent amounts to be added for bringing about the resultscharacterizing the invention, are almost negligible (0.05 by weight)relative to the solution volume, The detergent is regenerated after theoil separation and, thus, is not lost, except for a certain very smallwaste. The volume of the washing solution is only a fraction of thevolume required for conventional cleaning and need not be changed.

It is not necessary, either, to control the chemical composition. Theneed of flushing water is abolished completely. Therefore, theinstallation is relatively small and space-saving, which is of adecisive importance for planning or placing the installation in thebuildings required therefor. Due to the complete absence of discharge,furthermore, the definite requirement with respect to environmentprotection has been satisfied, which according to the conventionalmethods would have involved a very high burden both from an economic andoperationtechnical point of view. The price of the washing solution isnot affected by the addition of the cheap detergent, i.e. the washingsolution costs as much as normal water, contrary to the conventionalmethod, at which trichloroethylene and the added detergent amounts (3%)command a high price which, of course, is increased substantially by thefrequent changes of the entire washing solution.

The example described has as its only purpose to facilitate theunderstanding of the invention without, however, restricting the same.

What I claim is:

1. A method of environment protective degreasing of stainless steel webmaterial which comprises the steps of,

mechanically removing impurities on the web surfaces; subjecting thesurfaces to a treatment with a washing solution consisting of water plusa detergent having an HLB value of at least 10;

simultaneously supplying kinetic energy in the form of mechanicallyinduced agitation to the web material and treating solution to form alabile emulsion of impurities in the solution;

transferring the emulsion to a separate settling space wherein saidkinetic energy supply ceases;

heating the quiescent emulsion whereby the water detergent solutionportion thereof is separated from associated impurities and thedetergent solution is regenerated;

flushing the surfaces of the web material with a clean detergentsolution; and

mechanically removing adhering film of clean detergent solution from thesurfaces of the web material thus treated.

2. A method according to claim 1 characterized in that the flushing iscarried out with a clean washing solution by spraying.

3. A method according to claim 1, characterized in that the separationof the emulsion takes place in a settling space, which simultaneouslyserves as a sedimentation and storage tank.

4. A method according to claim 1, characterized in that the treatmenttakes place in a closed circuit process by means of suitable pumps, forachieving the environment protective object, without discharge into air,ground or water.

5. The method defined in claim 1, in which the detergent used includes adetergent having a non-ionic nature.

6. The method defined in claim 1, in which the detergent used is acomposition including both a nonionic compound and a detergent selectedfrom the group consisting of anionic and cationic compounds.

7. A method according to claim 1, wherein the detergent quantity addedto the water amounts to from 0.001% to 1.00% by weight.

8. The method defined in claim 1, wherein the temperatnre in thesettling space andi'during'the entire process is between 30 C. and 80 C.

References Cited UNITED STATES PATENTS 2,158,694 5/1939 Fenton "134-9 6Keogh 13410 X Groom 134-10 Croft 134-9 Quigley 134-9 Nachtman 134-9 U XUS. Cl. X.R.

